Field of the Invention
This invention relates to an image forming apparatus and a control program for an image forming apparatus. More specifically, this invention relates to an image forming apparatus and a control program for an image forming apparatus, wherein the image forming apparatus includes a photo conductor drum having a cylindrical shape and a developing device.
Description of the Related Art
As electrophotography image forming apparatuses, there are an MFP (Multi Function Peripheral) with a scanner function, a facsimile function, a copying function, a function of a printer, a data transmitting function and a server function, a facsimile device, a copying machine, a printer, and so on.
Generally, an image forming apparatus develops an electrostatic latent image formed on an image supporting body, to form a toner image, transfers the toner image onto a sheet, and fixes the toner image on the sheet by using a fixing device, to form an image on the sheet. Some image forming apparatuses develop an electrostatic latent image formed on a photo conductor drum by using a developing device to form a toner image, transfer the toner image onto an intermediate transfer belt by using a primary transfer roller, and transfer second the toner image on the intermediate transfer belt to a sheet by using a secondary transfer roller. According to such the apparatuses, the photo conductor drum and the intermediate transfer belt shall be image supporting bodies.
Density of images formed on sheets by an image forming apparatus may change, due to the fatigue of an image supporting body such as a photo conductor drum with elapsed time, the temperature and humidity change around the image forming apparatus, and so on. A technique to stabilize image density is proposed. More specifically, a test patch of toner is formed on the image supporting body. The adhesion amount of the toner is detected. The developing bias is appropriately controlled, to control the adhesion amount of toner.
For example, the document 1 below discloses a technique for configuration of developing electrical potential to obtain images which have target density. Namely, a plurality of toner patch images are formed on a photo conductor drum at an arbitrary interval, based on develop electrical potential obtained by the last high density correction. The developing electrical potential is configured by the image density.
[Document 1] Japan Patent Publication No. 2011-154146
According to an electro photographic process, developing properties fluctuate along a circumferential direction of a photo conductor drum, when toner is transferred from a developing device (a developing roller) to the photo conductor drum, due to rotational unevenness of the photo conductor drum. The rotational unevenness of the photo conductor drum is caused by eccentricity of the photo conductor drum due to mechanical tolerance. According to a conventional method, density ununiformity of test patches on the image supporting body occurs, due to rotational unevenness of the photo conductor drum. The detection error of the adhesion amount of toner is large. It causes deterioration in degree of accuracy of the toner adhesion amount control. It also has a problem in which the density can not be stabilized, since the image density fluctuates each time the adhesion amount of toner was controlled.
For users, density stability among pages is an important issue which determines the quality of images. Therefore, a control system that can stabilize image density is required.